v2.1.0: fix provenance warnings, clean install experience

Add package.json with openclaw plugin metadata, configure plugins.allow
in post-install.sh, and add source field to plugin manifest. Fresh
installs now load without trust/provenance warnings in gateway logs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

openclaw.plugin.json

@@ -2,7 +2,8 @@
   "id": "memory-continuity",
   "name": "Memory Continuity",
   "description": "Preserves working state across /new, reset, compaction, and gateway restarts via a simple markdown checkpoint file.",
-  "version": "2.0.0",
+  "version": "2.1.0",
+  "source": "https://github.com/dtzp555-max/memory-continuity",
   "configSchema": {
     "type": "object",
     "additionalProperties": false,